Stilbocoris Bergroth, 1893

Kondorosy, Előd & Zámbó, András, 2021, The genus Stilbocoris in the Malagasy area (Hemiptera: Heteroptera: Rhyparochromidae), Zootaxa 5047 (4), pp. 416-430 : 417-419

Stilbocoris Bergroth, 1893

Stilbocoris Bergroth, 1893: 201 . Type species by monotypy: S. solivagus Bergroth, 1893 .

Stilbocoris: Carayon (1961: 713) (biology), Scudder (1962: 438) (new species), Carayon (1964: 4815) (biology), Slater (1964: 981) (catalogue), Wilcox & Slater (1969: 696) (nomina nuda, distribution), Linnavuori (1978: 79) (new species), Slater (1993: 377) (in key), Slater & O’Donnell (1995: 123) (catalogue), Kondorosy (2006: 117) (genus group keyed), Krüger (2019: 353) (distribution, morphology)

Redescription. Body oval to oblong oval, shiny (sometimes dorsally dull), mostly glabrous, sometimes with very short, sparse (rarely dense), erect setae.

Head triangular, punctation variable (sometimes with larger or smaller but well visible, dense punctures on entire dorsum, sometimes with impunctate areas, sometimes dorsum with confluent punctures appearing finely rugose, dull). Antenniferous tubercles short, one-seventh to one-fourth of eye length in dorsal view, divergent or subparallel. Antenna longer than half length of body, slender. Scape thickened in apical half, bending laterad, surpassing tip of head by at least half its length. Pedicel, basi- and distiflagellum linear, longer than scape. Eyes not large, adjacent to anterolateral angles of pronotum. Ocelli situated medio-posteriad of eyes, about as far from eyes as their diameter or somewhat farther. Bucculae tiny, ventrally reaching less than half width of labium, posteriad not reaching base of antenna.

Pronotum trapezoidal, sometimes almost rectangular; anterior collar absent; calli sometimes barely, mostly moderately elevated; lateral margin hardly laminate (at most approaching diameter of pedicel base, more often not wider than half of it); transverse impression mostly well developed, separating anterior and posterior lobes, lateral margin concave at impression; posterolateral angles more or less produced caudad, posterior margin either straight except laterally or finely arcuate; punctation of pronotum variable. Scutellum large, longer than wide, with more or less emergent Y-shaped elevation mostly free of punctures, always with relatively strong and dense punctures lat- erad of elevation, often the strongest of all. Clavus parallel, with 3 rows of punctures, inner one fainter and sparser than others; claval commissure much (2–5 times) shorter than scutellum. Corium with rows of punctures along both sides of vein Cu but far from each other, on border of exocorium and along membranal margin, otherwise with scattered punctures, area between vein R+M and row along Cu mostly free of punctures. Exocorium smooth, very narrow in basal half, in apical half broadened, body subparallel but broadest here (about at apex of scutellum). Apical margin of corium almost straight. Membrane surpassing apex of abdomen, veins hardly visible. Thoracic sterna always with dense and strong punctures usually also on metepimeroid (last one impunctate in most genera of Drymini and other Rhyparochromidae ).

All femora similarly thick, almost always without teeth but with stiff erect setae of various number and arrangement (always with an apical pair dorsally, mostly on profemora ventrally but sometimes on all femora); stiff erect setae of tibiae long, on protibiae with 1, on other tibiae with 4 rows in entire length; legs also with very fine decumbent pubescence.

Abdomen with more or less fine and dense or sparse decumbent setae. Lateral extremity of intersegmental suture between sternites IV and V directed anteriad then curving posteriad, not reaching lateral margin (as usual in Rhyparochromidae ). Lateral part of suture between sternites V and VI also strongly curved anteriad. With a pair of large, oval, pruinose spots on some of sternites IV–VI, about halfway between midline and lateral margin, hardly visible in species with densely pubescent abdomen. Trichobothria and spiracles of sternite V of abdomen arranged as usual in Drymini .

Discussion. Sharing all characters of the tribe, namely the arrangement of trichobothria and position of the abdominal spiracles, Stilbocoris belongs to Drymini . This tribe, however, is highly diverse, comprising 57 described genera. Several genera (discussed below) possess strong, stiff setae at least on the profemur (most of them on all femora), but lack teeth on profemora. These genera furthermore have narrow, almost carinate lateral margin on the pronotum, large scutellum and three rows of punctures on the clavus; their integument is usually shiny; the metepimeroid is densely punctate; and lateral portions of the intersegmental suture between abdominal sternites V and VI are curved strongly anteriad (the plesiomorphic character state within Drymini ). Altogether 9 genera share these features, the majority of them being distributed in the Oriental Region (with some species reaching the Austromalayan Region), one in the Palaearctic Region and only two have Afrotropical distribution: Stilbocoris and Parastilbocoris .

Stilbocoris is a heterogeneous genus, so its delimitation from the related genera is not easy. Most of the morphologically similar and apparently phylogenetically related genera are distributed in the Oriental Region. Borneodrymus Kondorosy, 2006 can be characterized among others by the long temporal area of the head (eyes are far removed from the pronotum) and very long slender legs. Kanigara Distant, 1906 is easy to separate too: its members have either a flat scutellum or a highly concave apical margin of the corium, and their pronotum is very faintly punctate, laterally convex or straight, without traces of a transversal furrow. Lemnius Distant, 1903 and Thebanus Distant, 1903 are very close to each other if not congeneric ( Woodward & Malipatil 1987, Kondorosy 1996); both possess a strongly concave inner part of the apical margin of the corium; both of them are similar to some Stilbocoris species , but the bifurcation of their Y-shaped carina is situated anteriad of the middle of the scutellum (in Stilbocoris always posteriad of it), and the scutellum is not longer than wide (in Stilbocoris it is always much longer). Heissodrymus Kondorosy, 2006 is also well recognizable: these large species (perhaps the largest in Drymini ) are elongate, with long, almost parallel-sided pronotum (1.1–1.3 times wider than long), and have clearly bulbous meso- and metapleura ( Stilbocoris species have hardly bulbous pleura, their pronotum is more trapezoidal and almost always shorter). Coracodrymus Breddin, 1901 lacks transverse impression on the pronotum, and the lateral margin of it is convex; the abdomen has a large pruinose spot on lateral part of sternites IV and V (in Stilbocoris species such spot is present as well but sometimes only on sternite V or also on sternite VI). Lamproplax Douglas & Scott, 1868 , the only Palaearctic genus of this group, is very hard to separate from Stilbocoris ; the most characteristic feature is the lack of any large pruinose spot on the sternites (but even if a spot is present it might be difficult to observe in some Stilbocoris species with almost dull abdomen); also the punctures of the scutellum posteriad of the Y-shaped carina are extremely large, only slightly narrower than diameter of pedicel, while in Stilbocoris these are although stronger than other punctures but much smaller than diameter of pedicel.

The only other Afrotropical genus belonging to this group, Parastilbocoris , is also very similar to Stilbocoris . Carayon (1964) separated both genera based on genital features, moreover the dull and very pubescent integument and the number and arrangement of stiff setae of metatibiae occurring in Parastilbocoris . However, species of the latter genus are perhaps not more closely related to each other than to some Stilbocoris species , and even the abovementioned features should be re-evaluated, because there are some undescribed Stilbocoris species with somewhat shorter and less dense pubescence, so the limits of both genera are not clear. Stilbocoris certainly needs a thorough revision because of the study of the described and the numerous undescribed species showed significant differences in genitalia and other morphological features (perhaps more genera are hidden under Stilbocoris , however, this is not the subject of this paper).